The invention relates to an improved arrangement of a picking comb used particularly in jet looms.
Jet looms operate in such a manner that a weft thread of warp width is picked through open sheds along a path formed by the picking comb within which the weft thread is propelled under the action of a pressure fluid such as pressure air or gas expanding from a main nozzle and/or active guide teeth. Within the warp width the picking of the weft thread is monitored by monitoring guide teeth of the picking comb. In fact, the picking comb is formed, on the one hand, of passive guide teeth and, further, of active and detecting guide teeth which are arranged in side-by-side relation so that, by being interconnected and, for example, attached to a sley, they constitute a compact assembly.
The known arrangements of picking combs are made in such a way that the guide teeth are arranged into sections of various lengths, at least in portions the sum of which gives the total warp width. These sections of the picking comb are arranged in several variations.
One of the known constructions of picking combs for jet looms uses common connecting mandrels onto which the guide teeth are fitted, the teeth being axially spaced by means of spacer plates and mutually tightened by connecting means so as to form an assembly or sections fastened to the sley.
In other known embodiments the guide teeth are arranged in a guiding groove of a bar, in which they are relatively fixed in an axial direction by means of pins which fit into respective holes provided on the face of the adjacent guide tooth, the guide teeth being fixed in the guiding groove, for example in a clamping manner, by means of screws and nuts.
In another known embodiment the picking comb is formed of guide teeth sections which are assembled for example of a combination of passive and active guide teeth, the next section being formed of passive and detecting guide teeth, and the other forming self-contained sections having a reduced number of, for example, passive, active and detecting guide teeth. The said sections are formed in such a way that the shanks of the guide teeth are mounted, for example, in a channel or groove of a bar on which they are arranged in a side-by-side relation, and for holding them in their proper positions they are secured in the channel, for example, by means of embedding cementing compounds. The channels, or alternatively bars, provided with the guide teeth are fastened to the sley. For assembling the guide teeth according to the last named embodiment centering mandrels are used onto which the guide teeth are fitted with their picking apertures and spaced from each other by distance inserts, for example, plates. To ensure accurate alignment of the exit slots of the picking apertures of the guide teeth centering mandrels are used, the profile of which coincides with the geometry of the profile of the picking aperture of the guide tooth; a guide is used, most often a distance plate, which is fitted into the exit slots of the guide teeth and then uniformly pushed home onto the circumference of the centering mandrel within the length of the section of the picking channel.
Disadvantages of the known embodiments of picking channels are due to their construction. A common feature of these picking channels is an exacting manufacture and assembly thereof. Even when assembly jigs are employed, it is difficult to comply with the required accuracy of axial alignment of the picking apertures of the guide teeth and accurate alignment of their exit slots; a lack of accurate alignment subsequently manifests itself by weaving faults. The weft thread under insertion and the pressure fluid then impinge against the protruding front surfaces of the guide teeth of the picking comb. In case the guide teeth become demaged, their removal is difficult. It is true enough that the developments endeavor to bring about an improvement, for example, by arranging the guide teeth into replaceable sections. However, most often the active and subsequently the monitoring guide teeth become soiled or damaged and although arranged in said replaceable sections, often together with the passive guide teeth, it is necessary to remove a whole section if their function becomes faulty. Such replacement and subsequent repair are difficult and, moreover, warp thread breakages often occur during these operations, which in turn result in a further extension of unproductive activities of the weaving process in addition to the obvious extra work involved.